1. Field of the Invention
The present invention relates to an information recording/reproduction apparatus for converting an information bit to a code bit in order to record information on a recording medium at a high density and to a coding method suitable to the recording medium.
The present invention further relates to an information recording method for recording and reproducing information in and from a multibeam recording/reproduction apparatus and a recording medium at high speed.
2. Description of the Related Art
The first embodiment of the prior art is the optical memory disclosed in Japanese Patent Publication No. 2-31330. In the case of this embodiment, an information bit is converted to a code bit by the so-called run length limited (RLL) code to record the code bit along a track. FIG. 12 shows a well-known (1, 7) RLL code conversion table. As shown in FIG. 13, for example, code bits according to the conversion rule and moreover converted by the so-called NRZ (nonreturn-to-zero) recording are serially recorded along a track 101. Recording for tracks 102 and 103 is performed in the same way.
The second embodiment of the prior art is the multibeam recording/reproduction apparatus disclosed in Japanese Patent Application laying open No. 2-247837. In the case of this embodiment, a first read signal is reproduced from a code bit by a first light beam, a second read signal is reproduced from a code bit of an adjacent track by a second light beam, and the second read signal is subtracted from the first read signal in order to decrease crosstalk caused by the adjacent tracks.
The third embodiment of the prior art is an information signal recording/reproduction apparatus disclosed in the official gazette as Japanese Patent Application No. laying open 4-341974. In the case of this embodiment, a video format signal is divided into three channel video signals and recorded by three multibeams.
However, when recording is performed in accordance with the coding rule of the first embodiment of the prior art, a reproduction error occurs due to crosstalk caused by adjacent tracks 102 and 103. For example, at the position of light spot A. "1" or "record mark" is read and no crosstalk occurs because the adjacent tracks 102 and 103 are "0" or "nonmark." This embodiment performs so-called NRZ recording by causing "1" to correspond to "record mark" and "0" to correspond to "nonmark."
However, the code of the adjacent track 103 is "1" for light spot B and the code bits of both the adjacent tracks 102 and 103 are set to "1" for light spot C. Crosstalk therefore occurs and causes a reproduction error.
To solve the above problem, the second embodiment of the prior art decreases crosstalk by using the above method. However, the second light beam necessarily reads the code bit of its adjacent track. Therefore, crosstalk also occurs in the second read signal due to its adjacent track and crosstalk cannot be completely eliminated even if the second read signal is subtracted from the first read signal.
A multibeam recording/reproduction apparatus has recently been proposed which records or reproduces data by using a plurality of light beams at high speed. The multibeam recording/reproduction apparatus simultaneously records or reproduces data for a plurality of sectors even though a single-beam recording/reproduction apparatus can record or reproduce data for only one sector at a time.
However, because data is conventionally recorded by the recording method of the first embodiment of the prior art, even the multibeam recording/reproduction apparatus requires the recording or reproduction time for one sector in order to record or reproduce data for one sector. That is, in the case of recording or reproducing data for a number of sectors equal to or fewer than the number of beams, it becomes impossible to increase the operation speed. Moreover, it is a matter of course that the recording or reproduction time for at least one byte is necessary to record or reproduce data for one byte. That is, the same applies to the case of recording or reproducing data for a number of bytes equal to or fewer than the number of beams.
The third embodiment of the prior art divides a video signal into three channels and records or reproduces data with three light beams. However, the dividing method or digital data for a computer is not disclosed at all. Moreover, because a discrimination signal is recorded on different time bases of adjacent tracks, it remains difficult to shorten the time for recording/reproduction a piece of video information.